Hydrophobic ZnO nanoparticles were synthesized by controlled chemical precipitation and incorporated into PMMA matrix by in situ bulk polymerization, giving PMMA-ZnO nanocomposites. The effects of semiconductor nanoparticles on the rate of polymerization, thermal, and optical properties of the nanocomposites were studied with respect to reference sample polymerized in absence of particles.

Particles having a sharp diameter distribution around 25 nm were precipitated via transesterification of zinc acetate dihydrate with 1-pentanol at 130 ºC. After the formation of crystal core, a mixture of tert-butylphosphonic acid (t-BuPA) and tetrabutyl ammonium acetate (TBuAc) was applied. t-BuPA coats the particle surface, quenches the particle growth, and hydrophobizes the particles whereas TBuAc prevents the formation of undesirable lamellar zinc t-butylphosphonate. The surface-coated particles were dispersed in methyl methacrylate and free radical polymerization was carried out at 60 °C using AIBN as initiator. The particles induce the termination of chain growth by degenerative chain transfer. This suppresses both the gel effect and the formation of chains having thermally labile linkages, which inevitably form under conventional polymerization conditions. Hence, the thermal stability of PMMA is improved when the polymerization proceeds in presence of the ZnO nanoparticles. Spin-coated films of these composites exhibit a distinct cut off of transmission at 370 nm towards shorter wavelengths due to the high absorption coefficient of ZnO. The particles contribute to turbidity in the visible region because of scattering originating from the refractive index mismatch of PMMA and ZnO. Detailed data on the optical properties of these nanocomposite films will be reported.

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